The present invention relates to the processing of unrolled donor substrate, which is coated either before or after unrolling with an organic layer so as to facilitate the transfer of organic material from a donor substrate to an OLED device.
In color or full-color organic electroluminescent (EL) displays, also known as organic light-emitting diode (OLED) displays or devices, having an array of colored pixels such as red, green, and blue color pixels (commonly referred to as RGB pixels), precision patterning of the color-producing organic EL media is required to produce the RGB pixels. The basic EL device has in common an anode, a cathode, and an organic EL medium sandwiched between the anode and the cathode. The organic EL medium may consist of one or more layers of organic thin films, where one of the layers is primarily responsible for light generation or electroluminescence. This particular layer is generally referred to as the emissive layer of the organic EL medium. Other organic layers present in the organic EL medium may provide electronic transport functions primarily and are referred to as either the hole transport layer (for hole transport) or electron transport layer (for electron transport). In forming the RGB pixels in a full-color organic EL display panel, it is necessary to devise a method to precisely pattern the emissive layer of the organic EL medium or the entire organic EL medium.
Typically, electroluminescent pixels are formed on the display by shadow masking techniques, such as shown in U.S. Pat. No. 5,742,129. Although this has been effective, it has several drawbacks. It has been difficult to achieve high resolution of pixel sizes using shadow masking. Moreover, there are problems of alignment between the substrate and the shadow mask, and care must be taken that pixels are formed in the appropriate locations. When it is desirable to increase the substrate size, it is difficult to manipulate the shadow mask to form appropriately positioned pixels. A further disadvantage of the shadow mask method is that the mask holes can become plugged with time. Plugged holes on the mask lead to the undesirable result of non-functioning pixels on the EL display.
A method for patterning high-resolution organic EL displays has been disclosed in U.S. Pat. No. 5,851,709 by Grande et al. This method is comprised of the following sequences of steps: 1) providing a substrate having opposing first and second surfaces; 2) forming a light-transmissive, heat-insulating layer over the first surface of the substrate; 3) forming a light-absorbing layer over the heat-insulating layer; 4) providing the substrate with an array of openings extending from the second surface to the heat-insulating layer; 5) providing a transferable, color-forming, organic donor layer formed on the light-absorbing layer; 6) precision aligning the donor substrate with the display substrate in an oriented relationship between the openings in the substrate and the corresponding color pixels on the device; and 7) employing a source of radiation for producing sufficient heat at the light-absorbing layer over the openings to cause the transfer of the organic layer on the donor substrate to the display substrate. A problem with the Grande et al. approach is that patterning of an array of openings on the donor substrate is required. This creates many of the same problems as the shadow mask method, including the requirement for precision mechanical alignment between the donor substrate and the display substrate. A further problem is that the donor pattern is fixed and cannot be changed readily.
Using an unpatterned donor substrate and a precision light source, such as a laser, can remove some of the difficulties seen with a patterned donor. Littman and Tang (U.S. Pat. No. 5,688,551) teach the patternwise transfer of organic EL material from an unpatterned donor sheet to an EL substrate. A series of patents by Wolk et al. (U.S. Pat. Nos. 6,114,088; 6,140,009; 6,214,520 and 6,221,553) teaches a method that can transfer the luminescent layer of an EL device from a donor element to a substrate by heating selected portions of the donor with a laser beam.
Such a donor sheet works well for preparing small OLED devices. It can become difficult to handle for larger (greater than 15 cm) OLED devices or when a single manufacturing step prepares multiple OLED devices. Typical donor support material is supplied in roll form. One of the problems in handling an unrolled donor substrate is that it must be held relatively flat and wrinkle-free during organic coating, laser transfer, and transport. It is difficult to coat such a donor substrate evenly when it is not completely flat.
It is therefore an object of the present invention to provide a way of handling an unrolled donor substrate such that it is held relatively flat and wrinkle-free during organic coating, laser transfer, and transport.
This object is achieved by a method for tensioning unrolled donor substrate to facilitate transfer of organic material to form a layer on the unrolled donor substrate, comprising the steps of:
a) delivering of a portion of the unrolled donor substrate from a roll to a frame disposed in an organic coating chamber, such frame defining an aperture;
b) engaging the unrolled donor substrate and tensioning such material using a first clamp assembly associated with the frame;
c) coating the tensioned donor substrate with an organic layer in the organic coating chamber; and
d) cutting the unrolled tensioned portion of donor substrate into a sheet before or after it has been coated with organic material.
This object is also achieved by a method for tensioning unrolled donor substrate coated with at least one organic layer to facilitate transfer of organic material to an OLED substrate from the unrolled donor substrate, comprising the steps of:
a) delivering of a portion of the unrolled donor substrate from a roll to a frame;
b) engaging the unrolled donor substrate and tensioning such material using a first clamp assembly associated with the frame;
c) cutting the unrolled tensioned portion of donor substrate into a sheet.
In the present invention, an unrolled donor substrate material that can be coated with an organic layer either before or after unrolling is handled to facilitate the transfer of the organic layer onto an OLED substrate. It is an advantage of this method/apparatus that it maintains the tension of an unrolled donor substrate when a portion of the unrolled donor substrate is cut into a sheet, thus maintaining the donor free of wrinkles and sag. It is a further advantage that this tension can be maintained throughout further steps in the process. It is a further advantage that this tension can be maintained with no clamps or obstructions above the top surface, thus leaving this surface unobstructed for further operations. It is a further advantage that attachment of the unrolled donor substrate to the frame can be automated easily.